I may be way off base here, but I don't think it's that easy. The side-oiler blocks have an external
oil channel cast into the outside of the left (driver's) side of the block, which was then bored out to allow passage of the
oil from the front to rear. The
oil is then sent from the fore-aft passage, into the area between the crankshaft and camshaft bearing webs, and from there through drilled passages connecting the main and cam bearings. The top-oiler blocks do not have the main channel passage as part of their casting. I suppose it would be possible to tap and drill the outside of the block and add external lines, then plug off the unused top-oiler lines, but it would certainly result in a "funny looking" block. If you aren't going to race the block, the top-oiler system is adequate for street use. If you want to race it, you might want to keep looking for a side-oiler. My humble opining, anyway. You might want to talk to one or more of the FE experts which frequent this forum, such as George Anderson at Gessford or Bill Parham at Southern Automotive to see if they have done a successful conversion of this type.